Relations between workers and management have since deteriorated to the extent that one worker and union leader filed a complaint with police claiming he had been kidnapped and beaten up. Others have also claimed to have suffered mistreatment while protesting about working conditions.

M&S says it has now dropped the company for "commercial" reasons, but has remained in contact attempting to resolve the disputes. It denies that workers have suffered intimidation.

The Observer investigation focused on two factories in Gurgaon, one used by M&S and the other by Gap and Next, and found staff working up to 16 hours a day. All the retailers launched inquiries into the abuses and pledged to end excessive overtime.

M&S said it had found examples of excessive overtime being worked earlier in the year, but it had tackled the problem. Its own audits also flagged up other problems, which it described as "high-risk issues in documentation and conditions". These are understood to include the provision of water and toilet facilities for workers.

Since the publication of the investigation, there have been a number of reports of clashes between workers and management. British campaign group Labour Behind the Label spoke to workers and claims that 16 women were hurt in clashes outside the gates.

In a statement the group said that the clashes followed "several months of campaigning by the Garment and Allied Workers Union to get improvements in conditions at Viva Global. Workers complained of excessive and forced overtime, low wages, a lack of water to drink and in the toilets".

In a statement, M&S said it had conducted its own investigation into the allegations and could find no evidence to substantiate the claims being made against Viva Global.

A spokesman said: "M&S no longer sources from Viva Global. For commercial reasons only, we have not placed any orders with this factory since May and have no pending orders. All M&S production ended in August."